10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions

10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions — page 5 — into direct current DC a process called rectification Diodes were originally designed for use in AM radio receivers to rectify radio frequency signals but are now used in many different applications where electrical current must flow in only one direction For example diodes in many consumer electronics help protect the circuitry against batteries inserted backward Most of the time however the diode aspect of an LED is not important The rest of the name light-emitting simply means that this type of diode is designed to light up when electricity passes through How lEDs Work An LED is a semiconductor device built with crystalline metals like silicon and germanium plus small amounts of impurities that change the characteristics of the material These impurities are added to the semiconductor in a process called doping The added element called the dopant changes the base material into either a p-type or n-type semiconductor The distinction between p-type and n-type depends on whether the dopant adds excess free electrons or causes a deficit of free electrons The place where these two types of doped semiconductor meet is called the P-N junction and this is where light is created Electrical energy passing through the junction excites some of the charge carriers which emit light when they return to their nonexcited state in a process called electroluminescence The exact chemical composition of the semiconductor mate rial determines the band gap of the materials involved which in turn determines the color of light produced The first LEDs developed in the 1960s emitted light in the infrared end of the color spectrum which is invisible to the human eye but still useful for scientific experi ments Later developments of other semiconductors and dopants introduced new visible colors resulting in mass production of red LEDs in the late 1960s and yellow LEDs in the early 1970s A high-brightness blue LED was very difficult to develop and was considered the Holy Grail of the LED world until 1994 when three Japanese scientists finally figured out the secret to a blue LED They received the 2014 Nobel Prize in physics for this accomplishment 3 i n t rO d u c t i O n

10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions — page 7 — Figure 2 A bicolor LED has two LEDs connected anode-to cathode A bicolor LED contains two LEDs in the same two-lead package typically with the individual LEDs connected anode-to-cathode as shown in Figure 2 Usually the two LEDs have different colors enabling the circuit to display two different colors using only two leads For example if cur rent travels through the circuit from left to right the lower LED turns on If current travels through the circuit from right to left the upper LED turns on Another fun type is the candle flicker LED which contains a small computer chip that turns the LED on and off in a flickering pattern designed to emulate the natural flicker of a candle You’ve probably seen these LEDs at fancy restaurants or wedding receptions or anywhere you want to have the ambiance of a candle without the risk of fire red-green-blue lED The red-green-blue RGB LED packages three LEDs into one and actually allows you to create a whole spectrum of colors not just red green and blue For example you can combine red and green light to make yellow green and blue light to create cyan and red and blue light to make violet Mixing all three colors of light at the same intensity produces white light By combining these three colors of light at varying levels of brightness for each individual color you can make millions of colors this is the same method your TV and phone use to display full-color images Usually to vary the brightness each color is switched on and off very rapidly which tricks our eyes into seeing each color at a different level of intensity The simplest RGB LED has four connec tions one for each of the three colors plus one connection common to all three LEDs This common connection can be either a common anode CA or common cathode CC which describes the internal connections of a four-pin RGB LED Figure 3 shows a diagram of the connections of a common anode RGB LED 5 i n t rO d u c t i O n

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